There have been available various methods such as direct printing, shrink wrapping and label adhering to achieve a decorative effect, a content indication etc. for a container after the container has been injection molded.
The direct printing method is to roll a printing roller (2) directly on the side wall of the container (1) as illustrated by FIG. 16, the shrink wrapping method is to wrap the container (1) with shrinkable film (3) as illustrated by FIG. 17 and the label adhering method is to stick a printed label (4) on the container (1) as illustrated by FIG. 18, respectively of the attached drawings.
The conventional in-mold labeling method for the injection molded container is generally to load a label (7) comprising a bottom wall section (5) and side wall sections (6) into an injection mold and then to effectuate desired labeling with injected resin, as illustrated by FIG. 19. The alternative method is also well known, according to which the opposite side edges (6a), (6a) of the label (7) are joined to each other with synthetic resin as illustrated by FIG. 20.
However, the direct printing method as illustrated by FIG. 16 is disadvantageously poor in its expressive effect, the shrink wrapping method as illustrated by FIG. 17 requires a secondary process with a result of an increased cost, and the label adhering method as illustrated by FIG. 18 also requires a secondary process and correspondingly increases a cost.
As far as a need for the secondary process is concerned, the in-mold labeling method has been more advantageous than the remainder methods as illustrated by FIGS. 16, 17 and 18, respectively, since the labeling and the container molding simultaneously occur and therefore no secondary process has been required. However, the conventional in-mold labeling method has been accompanied with unsolved problems as will be described. For example, the conventional method of in-mold labeling has been effective for a cubic container having a side wall consisting of plane surfaces as seen in FIG. 19 but ineffective for a container having a curved side wall. For a legged container, it has been difficult for the conventional method of in-mold labeling to achieve the labeling on respective projecting legs for the structural reason.
With the method of FIG. 20, according to which the opposite side edges of the label are joined to each other, it has certainly been possible to provide even the curved surfaces with the desired labeling but the label has had to be relatively thick to accommodate the joining process, with a result of an increased cost.
According to the conventional method of in-mold labeling for the legged container, as will be apparent from FIG. 21 (A), a flow of injected resin as indicated by arrows occurs in the proximities of respective curved corners during flowing from a passage (10) to a passage (11) both defined between a core (8) and a cavity (9) of the mold and consequently a partial quantity of injected resin is apt to be forced out onto an outer surface of the label's side wall (6), because a lower end (6E) of the label's side wall (6) is at a level higher than the container's bottom (1B) in the proximities of the respective curved corners of the container (1). With a disadvantageous consequence, a partial quantity of injected resin has often been forced out onto the outer surface of the label or the label has often been creased with wrinkles.
Accordingly, it is a principal object of the invention to provide a method of in-mold labeling allowing the side wall of a container composed of curved surfaces alone or of curved surfaces and plane surfaces to be provided with in-mold labeling by forcing a label against a cavity side of the mold under an effect of the resin flow and the container produced by this method.